Adjustable posterior spinal column positioner

ABSTRACT

Height-adjustable devices suitable for insertion between posterior spinal processes that allow the surgeon to post-operatively adjust the height of the implant.

BACKGROUND OF THE INVENTION

The leading cause of lower back pain arises from rupture or degenerationof lumbar intervertebral discs. Pain in the lower extremities is causedby the compression of spinal nerve roots by a bulging disc, while lowerback pain is caused by collapse of the disc and by the adverse effectsof articulation weight through a damaged, unstable vertebral joint.

In some cases, when a patient having a collapsed disc moves in extension(e.g., leans backward), the posterior portion of the annulus fibrosis orfolding of the ligamentum flavum may further compress and extend intothe spinal canal. This condition, called “spinal stenosis”, narrows thespinal canal and causes impingement of tissue upon the spinal cord andnearby nerves, thereby producing pain.

The “80/20” rule of spine biomechanics postulates that the posteriorcolumn of the spine supports about 20% of axial spinal forces. Themuscles and ligaments in the posterior column experience tensile forcesin normal spine anatomy. However, in some cases of disc replacement, theaxial loads borne by the anterior and posterior columns becomeunbalanced. By developing an implant that re-introduces those naturaltensile forces, the 80/20 balance is re-established.

There have been numerous attempts to provide relief for theseafflictions by providing a spacer that inserts between adjacent spinousprocesses present in the posterior portion of the spinal column. Thisspacer essentially lifts the upper spinous process off of the lowerspinous process, thereby relieving stenosis. In general, theseinterspinous implants are adapted to allow flexion movement in thepatient, but resist or limit extension.

U.S. Pat. No. 6,068,630 (“Zuchermann”) discloses a spinal distractionimplant that alleviates pain associated with spinal stenosis byexpanding the volume in the spinal canal or neural foramen. Zuchermanndiscloses a plurality of implants having a body portion and lateralwings. The body portion is adapted to seat between the adjacent spinousprocesses, while the wings are adapted to prevent lateral movement ofthe body portion, thereby holding it in place between the adjacentspinous processes.

U.S. Pat. No. 5,645,599 (“Samani”) attempts to relieve spinal stenosisby essentially inserting a flexible horseshoe-shaped device between theadjacent spinous processes. Although the Samani device desirablyprovides a self-limiting flexibility, it nonetheless suffers from someinadequacies. For example, the Samani device does not provide forpost-operative adjustment.

In sum, conventional interspinous spacers lack post-operativeadjustability.

SUMMARY OF THE INVENTION

The present inventors have developed a number of height-adjustabledevices suitable for insertion between posterior processes. Thesedevices will give the surgeon the ability to alter the height betweenadjacent spinous processes by a segmental approach that is minimallyinvasive.

In a first embodiment, the device comprises a pair of hooks connected toa rod, wherein the hooks are adapted to be translatable along the rod.

In a second embodiment, the devices comprises two parallel plates and atelescoping cylinder-annulus feature therebetween that is movableaxially and in the opposite direction from one another.

In a third embodiment, the device comprises a driving mechanism such asan internal gear system that axially separates the upper and lowerhalves of the implant.

In a fourth embodiment, the device comprises upper and lower insertionholes adapted for receipt of adjustment rods that axially separate theupper and lower halves of the implant.

In a fifth embodiment, the device comprises a threaded projection and acorresponding threaded recess that axially separate the upper and lowerhalves of the implant. Preferably, one of these components is magnetic,thereby allowing for non-invasive adjustment.

In a sixth embodiment, the device comprises two parallel plates and abellows therebetween that is axially expandable.

Therefore, in accordance with the present invention, there is providedspinal implant for insertion into a space between adjacent posteriorprocesses, the implant comprising:

-   -   a) an upper body having:        -   i. an upper bearing surface for bearing against a first            posterior process, and    -   b) a lower body having:        -   i. an lower bearing surface for bearing against a second            posterior process, the upper and lower bearing surfaces            defining a height of the implant, and    -   c) means for adjusting the height of the implant.

For many patients, adjusting the height of the implant would bebeneficial because it would alow the surgeon to monitor pain of thepatient and adjust the space between adjacent spinous processes,transverse processes or facet joints to relieve pain, or accommodate forgrowth or changes in the pathologies to be treated.

In some embodiments, the adjustable device of the present invention canalso having an angular adjustment component, thereby allowing thesurgeon to correct scoliosis, or extreme lordotic or kyphotic curves, bya segmental approach, thereby avoiding a fusion of the anterior column.

DESCRIPTION OF THE FIGURES

FIG. 1 a discloses a cut-out view of an interspinous implant whose upperand lower bearing surfaces are separable by actuation of a gearmechanism.

FIG. 1 b discloses a posterior view of the complete implant of FIG. 1 a.

FIGS. 2 a-2 d disclose posterior, posterior cross-sectional, explodedisometric and top axial cross-sectional views of a device of the presentinvention.

FIG. 3 discloses an exploded isometric view of another embodiment of thepresent invention.

FIG. 4 discloses an interspinous implant whose upper and lower bearingsurfaces are separable by a telescoping mechanism.

FIG. 5 discloses an interspinous implant whose upper and lower bearingsurfaces are separable by translatable hooks.

FIGS. 6 a and 6 b disclose side and posteior views of an embodiment ofthe present invention using hooks and slidable bodies.

FIG. 7 a discloses an interspinous implant whose upper and lower bearingsurfaces are separable by the insertion and spreading of distractionrods.

FIG. 7 b discloses a bottom view of FIG. 7 a.

FIG. 8 discloses an interspinous implant whose upper and lower bearingsurfaces are separable by a rotation of a thread.

FIG. 9 discloses an interspinous implant whose upper and lower bearingsurfaces are separable by inflation of a bellows.

FIG. 10 is a prior art diagram of a natural functional spinal unit.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1 a and 1 b, there is provided an interspinousimplant 1 for insertion into an interspinous space between a first andsecond spinous process, the implant comprising:

-   -   a) a first body 11 having:        -   i. an upper bearing surface 13 for bearing against a first            spinous process,        -   ii. an outer side surface 15 having upper 16 and lower 18            extensions extending therefrom in the axial direction,        -   iii. an inner surface 17,        -   iv. a gear 19 attached to the inner surface and having a            first set of teeth 21,    -   b) a second body 31 having:        -   i. a lower bearing surface 33 for bearing against a second            spinous process,        -   ii. an outer side surface 35 having upper 36 and lower 38            extensions extending therefrom in the axial direction, and        -   iii. an inner surface 37 having a second set of teeth 41            wherein the upper surface and the lower bearing surfaces            define a height of the implant, and wherein the sets of            teeth cooperate such that, upon rotation of the gear, the            upper bearing surface moves relative to the second bearing            surface, thereby changing the height of the implant.

Because adjustability is desirable only at selected times, it isdesirable that the implants of the present invention further contain ameans for rendering the height non-adjustable. In preferred embodiments,a locking mechanism (such as a set screw) is positioned to contact theset of teeth on the gear and may be used to essentially stop theratcheting nature of the rack-and-pinion components.

In one embodiment, the implant further comprises a set screw 45 and thesecond body has a threaded hole for accommodating a set screw, whereinthe threaded hole runs from the outer surface of the second body hook tothe gear teeth. Accordingly, the set screw can be percutaneouslymanipulated in order to allow or prevent height adjustability.

A set screw can also be used to close the gap between the two extendingbodies, thereby stopping the rotation of the gear.

In some embodiments, as in FIG. 1, the one of the bodies has an axialalignment flange 47 and the other body has an alignment rail. Thealignment flange nests in the rail and these features cooperate toinsure that rotational movement of the gear is translated into purelylinear relative movement of the bodies. In other embodiments, apin-and-slot mechanism may be used to accomplish the same goal.

In some embodiments, an actuation rod (not shown) is attached to thecenter of the gear and extends to the surface of the implant. Therefore,the gear can be actuated by rotating the actuation rod. This allows forpercutaneous actuation of the height-adjustable implant. In preferredembodiments, the proximal end portion of the rod has a hexagonal port49.

In some embodiments, the gear can be magnetic, and thus susceptible torotation when under the influence of a magnetic field. In suchembodiments, there is no need for a driver access port on the implantfor actuating the gear.

In preferred embodiment, the bearing surface 33 of one of the bodiesextends substantially entirely to the inner side 20 of the opposingextension 18 of the other body. When the bear surface extends so far,the implants maximizes the surface area with which it can support theadjacent processes, thereby minimizing stress upon the implant.

In another embodiment of the present invention using gears to producetranslation of opposed surfaces and effect height adjustment, andreferring now to FIGS. 2 a-2 d, there is provided an interspinousimplant 801 for insertion into an interspinous space between a first andsecond spinous process, the implant comprising:

-   -   a) a first body 811 having:        -   i. an upper bearing surface 813 for bearing against a first            spinous process,        -   ii. an outer side surface 815 having upper 816 and lower 818            extensions extending therefrom in the axial direction,        -   iii. an inner surface 817,        -   iv. a gear 819 attached to the inner surface and having a            first set of teeth 821,    -   b) a second body 831 having:        -   i. a lower bearing surface 833 for bearing against a second            spinous process,        -   ii. an outer side surface 835 having upper 836 and lower 838            extensions extending therefrom in the axial direction, and        -   iii. an inner surface 837 having a second set of teeth 841            wherein the upper surface and the lower bearing surfaces            define a height of the implant, and

wherein the sets of teeth cooperate such that, upon rotation of thegear, the upper bearing surface moves relative to the second bearingsurface, thereby changing the height of the implant.

In some embodiments, as best seen in FIG. 2 c, first body 811 mayoptionally include two half-bodies 812 and 814. When provided in thisconfiguration, a set screw 845 may be inserted across each half-body (asshown in FIG. 2 d) and used to close or open the half-bodies. In theiropen position, the half-bodies do not interfere with the rotation ofgear 819. In their closed position, however, the half-bodies preventrotation of the gear.

In some embodiments (as in FIG. 2 d), the first and second bodies areadapted to possess a T-slot guiding mechanism 847, comprising a T-slotand a corresponding T-projection. These features are provided to controlthe extension of the first and second bodies. In some cases using theT-slot and T-projection, extension of the two bodies can be controlledby the gear (as shown), while in others, extension can be controlled bya distraction device.

In other embodiments, a dovetail feature may be provided on the firstand second bodies for guiding the extension.

In another embodiment of the present invention using a distractiondevice and translation of opposed surfaces to effect height adjustment,and referring now to FIG. 9, there is provided an interspinous implant51 for insertion into an interspinous space between a first and secondspinous process, the implant comprising:

-   -   a) a first body 61 having:        -   i. an upper bearing surface 63 for bearing against a first            spinous process,        -   ii. outer side surfaces 65,        -   iii. upper extensions 66 extending from the outer side            surfaces in the axial direction,        -   iv. a longitudinal recess 70 extending into each outer side            surface and upper extension in the transverse direction, and        -   iv. a first plurality of holes 69 adapted for attachment to            an insertion instrument,    -   b) a second body 81 having:        -   i. a lower bearing surface 83 for bearing against a second            spinous process,        -   ii. a recess 84 defining inner side surfaces 85,        -   iii. lower extensions 88 extending from each inner side            surface in the axial direction,        -   iv. longitudinal projections 90 extending from each inner            side surface and lower extension in the transverse            direction,        -   v. a second plurality of holes 89 adapted for attachment to            an insertion instrument,            wherein the upper surface and the lower bearing surfaces            define a height of the implant, and            wherein the longitudinal projection is adapted for slidable            reception within the longitudinal recess, so that the upper            bearing surface may move relative to the second bearing            surface, thereby changing the height of the implant.

In this embodiment, the slidable reception of the longitudinalprojection within the longitudinal recess allows the upper bearingsurface to move relative to the second bearing surface, thereby changingthe height of the implant.

In use, insertion instruments are inserted into the holes sets andeither a) moved toward one another to decrease the height of the deviceor b) moved away from one another to increase the height of the device.A set screw ( not shown) is preferably used to lock and unlock thelongitudinal projection/recess assembly.

Now referring to FIG. 4, there is provided an interspinous implant 201for insertion into an interspinous space between an upper and lowerspinous process, the implant comprising:

a) a lower base 211 having a lower bearing surface 213 adapted forfixation to an upper side of the lower spinous process and an uppersurface 215,

b) an upper base 221 having an upper bearing surface 223 adapted forfixation to a lower side of the upper spinous process and a lowersurface 225, and

c) a height-adjustable container 231 having a lower portion attached tothe lower base and an upper portion attached to the upper base.

In this particular embodiment, the height-adjustable containercomprises:

-   -   i) an upper projection (here, a cylinder) 233 having an upper        surface 235 attached to the lower surface of the upper base and        an outer radius, and    -   ii) a lower recess (here an annulus) 237 having a lower surface        239 attached to the upper surface of the lower base, and having        an inner radius,        wherein the outer and inner radii are adapted to provide a        telescoping action in the height adjustable container.

In some embodiments, as in FIG. 9, the telecopic action means may bereplaced by a bellows 601. Preferably, the bellows comprises a portadapted for the introduction of a fluid.

As above, this implant may also further contain a means for renderingthe height non-adjustable. In preferred embodiments, a set screw may beused to contact each of the annulus and cylinder components toessentially stop the telescoping action.

In some embodiments, the height of the container may be adjusted byaltering an amount of fluid disposed within the container cavity. Thefluid may be a liquid, gas or gel.

Referring now to FIG. 5 a, there is provided an interspinous implant 301for insertion into an interspinous space between adjacent posteriorprocesses, comprising:

-   -   a) a central longitudinal body 303 having a diameter and first        305 and second 307 ends defining a length at least as great as        the distance between adjacent posterior processes,    -   b) a first hook 311 having a bore 313 adapted for slidable        connection to the central longitudinal body and a concave        bearing portion 315 adapted for bearing against a first        posterior process, and    -   c) a second hook 321 having a bore 323 adapted for slidable        connection to the central longitudinal body and a concave        bearing portion 325 adapted for bearing against a second        posterior process,        wherein the first end of the central longitudinal body is        received within the first bore, and the second end of the        central longitudinal body is received within the second bore.

Because the concave bearing portions of the hooks of FIG.5 a open inopposite directions, the implant is desirably used to maintain theheight of a space, such as the interspinous space between adjacentspinous processes.

In this embodiment, each hook is shown as being slidable along the rod.Having two translatable hooks allows for twice as much of a maximumadjustability length; provides for more adjustment options when workingaround bony anatomy, and provides both increased flexibility andstability. However, in other embodiments, one of the hooks may be fixedto the central longitudinal body. Requiring that only a single hook beslidable reduces the time required to make the desired heightadjustment.

In this embodiment, the concave bearing portion of each hook is shown asbeing essentially in-line with the rod. This is advantageous because therod will be under compressive stresses. However, in other embodiments(not shown), the concave bearing portion of each hook may be offset fromthe rod axis. The offset nature of the hooks is advantageous because itallows the hooks to possess a greater range of travel along the rod.

Because adjustability is desirable only at selected times, it isdesirable that the implants of the present invention further contain ameans for rendering the height non-adjustable. In preferred embodiments,a locking mechanism , such as set screw 331, is positioned in a threadedbore within a hook, is adapted to contact the rod and may be used toessentially stop the slidable nature of the hooks.

In one embodiment, the implant comprises a set screw and each slidablehook has a threaded hole for accommodating a set screw, wherein thethreaded hole runs from the outer surface of the hook to the rod.Accordingly, the set screw can be percutaneously manipulated in order toallow or prevent height adjustability.

In some embodiments, each hook can include a hole on its posteriorsurface adapted for insetion of a tyne of a forceps instrument. When thetynes are inserted into these holes, manipulation of the separationdistances between the tynes adjusts the height of the implant.

In some embodiments, the rod or gear can be magnetic, and thussusceptible to rotation when under the influence of a magnetic field. Insuch embodiments, the rod preferably includes a first thread thatthreadably mates with the threaded bore of first hook and a secondreverse thread that threadably mates with the threaded bore of thesecond hook

Now referring to FIG. 5 b, there is provided a height adjustableposterior implant that is substantially the same as that of FIG. 1 a,except that the concave bearing portions 341, 343 open in the samedirection, substantially transverse to the longitudinal axis of the rod.This implant is desirably fitted to adjacent transverse proceses inorder to compress the distance therebetween. Accordingly, it is believedthat this implant would have an advantageous use in correctingscoliosis, or in adjusting the angle of the anterior disc space to amore lordotic or kyphotic orientation.

Referring now to FIG. 6, there is provided an interspinous implant 301for insertion into an interspinous space between adjacent posteriorprocesses, comprising:

-   -   a) an upper body 911 having an upper bearing surface 917 adapted        for bearing against an upper posterior process and a        longitudinal shank 913 having a first plurality of teeth 915, a        locking hole 919 and a distraction hole 921, and    -   b) a lower body 931 having a lower bearing surface 937 adapted        for bearing against a lower posterior process and a longitudinal        shank 933 having a second plurality of teeth 935, a locking hole        939 and a distraction hole 951, and    -   c) a set screw 941 disposed within both of the locking holes,        wherein the first plurality of teeth engage the second plurality        of teeth.

The devices of the present invention may include conventional actuationmeans well known to the person of the ordinary skill in the art toadjust the height of the device.

In some embodiments, mechanical actuators are used. In one preferredexample, a percutaneous approach is used to deliver the distal end of adriver (e.g., screwdriver or hexdriver) to a port in the device. Uponrotation of the driver, the height of the implant is adjusted. See FIGS.1, 4 and 5.

Now referring to FIG. 7 a, there is provided an interspinous implant forinsertion into an interspinous space between an upper and lower spinousprocess, the implant comprising:

-   a) a first base 411 having an outer bearing surface 413 adapted for    fixation to an end of the first spinous process, an inner surface    415 and a first extension 403 extending from the inner surface,-   b) an second base 421 having an outer bearing surface 423 adapted    for fixation to an end of the second, an inner surface 425, and a    recess 405 in the inner surface,

wherein the extension is adapted for slidable reception within therecess

In some embodiments, the device comprises a plurality of holes locatedsubstantially on the same face of the implant and on upper and lowerportions of the implant. In the case of FIG. 7 a, three holes 401 areprovided on the upper portion of the implant, and three holes 402 areprovided on the lower portion of the implant. When compression ordistraction rods (not shown) having diameters corresponding to theirassociated holes are inserted into the holes, the height of the devicemay be adjusted by increasing or reducing the distance between the rods.In the case of FIG. 4 a, the height of the implant is adjusted by thetelescoping action produced by cylinder 403 and annulus 405.

Now referring to FIG. 7 b, in preferred embodiments, the holes extend atleast one-quarter of the depth of the implant, more preferably at leastone-half the depth of the implant. This feature minimizes any cantilevereffect.

In some embodiments, the extension has an outer surface that is smooth.In others the extension has an outer surface that is threaded.

In some embodiments, the implant further comprises a set screw receivedwithin the second base and positioned to contact the extension.

In some embodiments, the implant has a magnetic component such that theheight adjustment can driven by movement of an external magnet. Theseembodiments are advantageous because the height adjustment may beaccomplished completely non-invasively.

In other embodiments, the device includes an internal motor capable ofbeing powered by an external magnetic field, also allowing heightadjustment to be accomplished completely non-invasively.

For example, and now referring to FIG. 8, there is provided aninterspinous implant 501 for insertion into an interspinous spacebetween an upper and lower spinous process, the implant comprising:

a) a lower base 511 having a lower bearing surface 513 adapted forfixation to an upper side of the lower spinous process and an uppersurface 515 having a threaded recess 517 therein,

b) an upper base 521 having an upper bearing surface 523 adapted forfixation to a lower side of the upper spinous process and a lowersurface 525 having a smooth recess 527 therein, and

c) a longitudinal rod 531 having a lower portion 532 having a threadedend 533 and an upper portion 535 having a smooth end portion 537,

wherein the threaded end portion of the longitudinal rod is threadablyreceived in the threaded recess of the lower base, and wherein thesmooth end portion of the longitudinal rod is slidably received in thesmooth recess of the upper base.

In preferred embodiments, the slidable action of the upper smooth recessand rod end portion may be checked by a set screw 541 positioned tocontact the rod.

In some embodiments, the implant of FIG. 8 further comprises a pluralityof holes in each of the upper and lower bases, wherein the holes areadapted for attachment to a compression or distraction instrument.

In some embodiments, the extension of the implant of FIG. 8 has an outersurface that is smooth. In others, it has an outer surface that isthreaded.

In some embodiments, the implant further comprises a first set screwreceived within the first base and positioned to contact the rod. Insome embodiments, the implant further comprises a second set screwreceived within the second base and positioned to contact the rod.

In some embodiments, the implant has an expandable container such thatthe height adjustment can be achieved by adding a fluid to thecontainer, such as a liquid, gas or gel. These embodiments areadvantageous because the height adjustment may be accomplishedpercutaneuously with a high gauge needle.

In some embodiments (now shown), the deep portion of the recess includesa recessed lip projecting outward from the periphery of the recess, andthe deep end of the smooth end portion 537 of the rod 531 includes atransverse projection adapted to fit within the lip, but not within theremaining width of the recess. These features provide a stop thatinsures that the smooth end portion of the rod will not disengage fromthe recess.

The implants of the present invention may be used in many locationsabout the posterior portion of the human spine. In some embodiments, thedevice may be an interspinous device, adapted to be inserted betweenadjacent spinal processes. In others, the device may be adapted to beinserted between adjacent transverse processes. In others, the devicemay be adapted to be inserted between adjacent facets defining a facetjoint.

In some embodiments, the height-adjustable devices are used inconjunction with a devices placed on the anterior side of the spines,such as a disc replacement device, a nucleus pulposus augmentationdevice,or a fusion device such as a mesh or a cage. The use of aheight-adjustable posterior device with an anteriorly-placed device isadvantageous because it provides for a minimally invasive,post-operative correction of problems such as implant subsidence, rangeof motion, and pain.

The device may also be used for temporal tailoring of physiologicprocesses. For example, in one embodiment used in conjunction with ananterior device having surfaces adapted for bony ingrowth, the posteriordevice is inserted in a manner so as to compress the anterior portion ofthe spine, thereby speeding the bony ingrowth through the anteriordevice. After such in-growth occurs, the height of the posterior deviceis adjusted so as to lessen the compression experienced on the anteriorportion of the spine.

In other embodiments, the locking mechanism of the device may beloosened to allow for greater freedom of movement of the device.

In some embodiments, the height-adjustable device is implanted at thetime of implantation of the disc replacement device or nucleus pulposusaugmentation device. In others, the height-adjustable device isimplantation at the time of revision of the disc replacement device ornucleus pulposus augmentation device.

In most of the embodiments presented above, the upper and lower bearingsurfaces of the device are shown as being essentially flat. In otherembodiments, however, these surfaces are shaped to provide greatercorrespondence with the bony anatomy against which they bear. Forexample, when the device is an interspinous process, the bearingsurfaces may be concave in order to correspond with the convex nature ofthe opposing spinous processes. In other embodiments adapted forplacement within a facet joint, the bearing surfaces have a large radiusto correspond with the relatively large radius of the natural facets.

In most of the embodiments presented above, the adjustment results inessentially linear displacement of the upper and lower bearing surfacesof the device. In other embodiments, however, the adjustment meachanismsare adapted to provide angular displacement as well. For example, insome embodiments, the device has corresponding curved sliding surfaces,whereby their relatively movement causes a change in the relative angleof the upper and lower bearing surfaces. In some embodiments, thereofthe curved sliding surfaces are fromed by a polyaxial sphere-in-cuparrangement.

Although the locking means set forth above typically present a setscrew, other locking means may be employed. In some embodiments, thelocking mechanism may be selected from the group consisting of a setscrew, a spring-loaded ratchet-and-pawl, a spring-loaded pin-and-detent,and a wedged thread having spring-loaded balls. In some embodiments, thelocking mechanism is magnetic, so that the locking and unlocking of thelocking mechanism may be accomplished by an external magnet.

The devices of the present invention may be used advantageously in manysituations. For example, the height of the implant may be adjusted inorder to increase or decrease the spacing between spinous proceses untilthe desired patient result is obtained. For example, it may be adjustedto shift sections of the vertebral bodies until nerve compression orother pathology is reduced, thereby minimizing pain and obviating theneed for other invasive surgical procedures.

The height may be adjusted based upon pain feedback from the patient.

Multiple devices may be used in order to adjust multiple segments in thesame session. This would have advantage in the management of scoliosis(as it allows for incremental adjustments over time, and of pain andnerve impingement.

The height of the device may be adjusted to accommodate growth of thepatient.

The height of the device may be adjusted to reflect a change inpathology (e.g., as a degenerative disease progresses).

In cases wherein an anterior device has been implanted, the height ofthe posterior device may be adjusted in order to re-establish the proper80/20 load sharing balance. As noted above, the device of the presentinvention may also be used to initially deliberately load a graft placedin the anterior portion of the spine, and then adjusted to release theload once sufficient bone growth has occurred.

In some embodiments, the device of the present invention may include anadjunct feature designed to further patient outcome. For example, insome embodiments, the device may include an injection port for thedelivery of medications, such as narcotics. In some embodiments, thedevice may include electrodes for the facilitation of spinal nervestimulation or bone growth. In some embodiments, the device may includemagnets for bone growth promotion.

In some embodiments of the present invention, MEMS technology sensorsand actuators may be incorporated into the device allowing the physicianto make adjustments or gather data either automatically ortelemetrically.

In some embodiments, a battery may be used to drive the adjustmentmechanism of the device. In some embodiments thereof, the battery islocated internally, either within or adjacent to the implanted device.In others, the battery is located external to the patient and iselectrically connected to the device by a needle.

In some embodiments, the adjustment is actuated by a component havingshape memory capabilities. Such components have the ability tosuperelastically change their shapes in response to a temperaturechange. Therefore, when a device having a shape memory component isused, the surgeon will be able to adjust the height of the device bysimply changing the temperature of the shape memory component.

In some embodiments, the adjustment is actuated by a piezoelectriccomponent. Such components have the ability to vibrate in response toelectric current. Therefore, when a device having a piezoelectriccomponent is used, the surgeon will be able to adjust the height of thedevice by simply vibrating a piezoelectric component adapted to act asan actuator of a threaded component.

The implants of the present invention may be suitably manufactured fromany suitable biomaterial, including metals such as titanium alloys,chromium-cobalt alloys and stainless steel) and polymers (such as PEEK,carbon fiber-polymer composites and UHMWPE.

In some embodiments, the device is specifically manufactured for aspecific individual. In preferred embodiments thereof, an MRI of thepatient is taken, and is used as input to a computer-aided design (CAD)device to produce a device having at least one patient-specificcontoured surface. The contouring of that surface may be accomplishedconventional methods such as machining or casting.

Because of the dynamic nature of the device of the present invention, insome embodiments, there may be a concern that its expansion may producea new issue. For example, there may be a concern that expansion producesa newly created void in the device that may undesirably promote tissueingrowth. In another example, there may be a concern that expansion orheight reduction causes impingement of a surface upon a nearby nerve.

Therefore, in some embodiments, the device is encapsulated in anexternal housing (such as silicone). The housing preferably can bestretched in the amount desired in the expansion without generatingundue stress. In one preferred embodiment, the external housing covers abellows component of the device.

1. A spinal implant for insertion into a space between adjacentposterior processes, comprising: a) a central longitudinal body, b) afirst hook having a bore adapted for slidable connection to the centrallongitudinal body and a first concave bearing portion adapted forbearing against a first posterior process.
 2. The implant of claim 1further comprising: c) a second hook having a bore adapted for slidableconnection to the central longitudinal body and a second concave bearingportion adapted for bearing against a second posterior process.
 3. Theimplant of claim 1 further comprising: c) a second hook fixed to thecentral longitudinal body and a second concave bearing portion adaptedfor bearing against a second posterior process.
 4. The implant of claim3 wherein the central longitudinal body defines a longitudinal axis andwherein each of the first and second concave bearing portions arein-line with the longitudinal axis.
 5. The implant of claim 3 whereinthe central longitudinal body defines a longitudinal axis and whereineach of the first and second concave bearing portions are offset fromthe longitudinal axis.
 6. The implant of claim 1 further comprising alocking mechanism positioned to contact the central longitudinal body.7. The implant of claim 3 wherein the first and second concave bearingportions open in opposite directions.
 8. The implant of claim 3 whereinthe first and second concave bearing portions open in the samedirection.
 9. The implant of claim 3 wherein the central longitudinalbody is selected from the group consisting of a magnetic body and agear.
 10. A spinal implant for insertion into a space between a firstand second posterior process, the implant comprising: a) a first bodyhaving: i. an upper bearing surface for bearing against a first process,ii. an outer side surface having upper and lower extensions extendingtherefrom in the axial direction, iii. an inner surface iv. a gearattached to the inner surface having a first set of teeth, b) a secondbody having: i. a lower bearing surface for bearing against a secondprocess, ii. an outer side surface having upper and lower extensionsextending therefrom in the axial direction, iii. an inner surface havinga second set of teeth, wherein the sets of teeth cooperate such that,upon rotation of the gear, the upper bearing surface moves relative tothe second bearing surface, thereby changing the height of the implant.11. The implant of claim 10 further comprising a locking mechanismpositioned to fix the gear.
 12. The implant of claim 10 furthercomprising an actuation rod attached to the center of the gear.
 13. Theimplant of claim 10 wherein the gear is magnetic.
 14. The impant ofclaim 10 wherein at least one bearing surface extends substantially toan inner side of an extension.
 15. A spinal implant for insertion into aspace between an upper and lower process, the implant comprising: a) alower base having a lower bearing surface adapted for fixation to anupper side of the lower spinous process, b) an upper base having anupper bearing surface adapted for fixation to a lower side of the upperspinous process, and c) a height-adjustable container having a lowerportion attached to the lower base and an upper portion attached to theupper base.
 16. The implant of claim 15 wherein the height-adjustablecontainer comprises: i) an inner projection having a surface attached toa surface of one of the the upper and lower bases, the projection havingan outer surface, and ii) an outer annulus having a surface attached toa surface of the other of the upper and lower bases, the annulus havingan inner surface, wherein the outer surface of the projection and innersurface of the annulus are adapted to provide a telescoping action inthe height adjustable container.
 17. The implant of claim 15 furthercomprising a locking mechanism adapted to contact each of the innerprojection and outer annulus.
 18. The implant of claim 15 wherein theheight-adjustable container defines a cavity, and wherein the cavitycontains a fluid.
 19. The implant of claim 15 wherein theheight-adjustable container comprises a bellows, wherein the bellows hasa port adapted for the introduction of a fluid.
 20. The implant of claim15 having an external housing.
 21. A spinal implant for insertion into aspace between adjacent posterior processes , the implant comprising: a)a first base having an outer bearing surface adapted for fixation to anend of the first posterior process, an inner surface and a firstextension extending from the inner surface, b) a second base having anouter bearing surface adapted for fixation to an end of the secondposterior process, an inner surface, and a recess in the inner surface,wherein the extension is adapted for slidable reception within therecess.
 22. The implant of claim 21 further comprising: c) a pluralityof holes in each of the upper and lower bases, wherein the holes areadapted for attachment to a distraction or compression instrument. 23.The implant of claim 21 wherein the extension has an outer surface thatis smooth.
 24. The implant of claim 21 wherein the extension has anouter surface that is threaded.
 25. The implant of claim 21 furthercomprising: c) a locking mechanism received within the second base andpositioned to contact the extension.
 26. A spinal implant for insertioninto a space between adjacent posterior processes, the implantcomprising: a) a first base having an outer bearing surface adapted forfixation to an end of the first posterior process, an inner surfacehaving a recess, b) an second base having an outer bearing surfaceadapted for fixation to an end of the second posterior process, an innersurface having a recess, c) a rod having a first end and a second end,wherein the rod is adapted for slidable reception within the recess. 27.The implant of claim 26 further comprising: d) a plurality of holes ineach of the upper and lower bases, wherein the holes are adapted forattachment to a distraction or compression instrument.
 28. The implantof claim 26 wherein the extension has an outer surface that is smooth.29. The implant of claim 26 wherein the extension has an outer surfacethat is threaded.
 30. The implant of claim 26 further comprising: d) afirst locking mechanism received within the first base and positioned tocontact the rod.
 31. The implant of claim 30 further comprising: e) asecond locking mechanism received within the second base and positionedto contact the rod.
 32. A spinal implant for insertion into a spacebetween adjacent posterior processes, the implant comprising: a) anupper body having: i. an upper bearing surface for bearing against afirst posterior process, and b) a lower body having: ii. an lowerbearing surface for bearing against a second posterior process, theupper and lower bearing surfaces defining a height of the implant, andc) means for adjusting the height of the implant.
 33. The implant ofclaim 32 wherein the means is selected from the group consisting oftranslating hooks, a telescoping component, a gear mechanism, upper andlower distraction holes, upper and lower threaded components, and abellows.
 34. A posterior spinal implant comprising: a) a first bodyhaving: i. an upper bearing surface, ii. outer side surfaces, iii. upperextensions extending from the outer side surfaces in the axialdirection, iv. a longitudinal recess extending into each outer sidesurface and upper extension in the transverse direction, and iv. a firstplurality of holes adapted for attachment to an insertion instrument, b)a second body having: i. a lower bearing surface, ii. a recess defininginner side surfaces, iii. lower extensions extending from each innerside surface in the axial direction, iv. longitudinal projectionsextending from each inner side surface and lower extension in thetransverse direction, v. a second plurality of holes adapted forattachment to an insertion instrument, wherein the upper surface and thelower bearing surfaces define a height of the implant, and wherein thelongitudinal projection is adapted for slidable reception within thelongitudinal recess, so that the upper bearing surface may move relativeto the second bearing surface, thereby changing the height of theimplant.
 35. A posterior spinal implant, comprising: a) an upper bodyhaving an upper bearing surface adapted for bearing and a longitudinalshank having a first plurality of teeth and a locking hole, and b) alower body having an upper bearing surface adapted for bearing and alongitudinal shank having a first plurality of teeth and a locking hole,and c) a set screw disposed within both of the locking holes, whereinthe plurality of teeth engage the second plurality of teeth.